Onsemi NCP1246 | Demoboard AND9170-D

Description

When designing power supplies, the important definingregulations for efficiency and no-load power requirementsare the ENERGY STAR® specifications. With the release ofthe EPS 2.0 standard, the light-load input powerconsumption and the standby power consumption havebecome more important. The new specification moreaccurately reflects the actual usage of a laptop adapter whichoperates a considerable amount of time in a no-load ora minimal load operating condition (laptop in sleep mode).The key losses need to be identified when focusing on thelight-load efficiency of the adapter design. Switching lossesplay a major role in determining the light-load efficiency andare directly linked to the control methodology. These lossesare caused by the energy stored in the sum of all thecapacitances at the drain node (MOSFET outputcapacitance, stray capacitance of the transformer and otherparasitic capacitances on PCB) together with the gate chargelosses associated with driving the MOSFET. These lossesare also proportional to the switching frequency. Hencereducing the switching frequency reduces the losses andimproves the efficiency.The NCP1244/46 family of PWM controllers are focusedon meeting the new stringent ENERGY STAR®requirements. A key part of this architecture is a frequencyfoldback function, thereby lowering the frequency at lighterloads and reducing the switching losses. The additionalfeature helping to decrease the switching losses is a fixedcurrent set point under light-loading condition. This featureincreases the transferred energy in a single pulse, but alsodecreases the switching frequency to deliver the requiredamount of power to the load.No-load input power of the power supply continues to bean important requirement. This refers to when the powersupply or adapter is plugged into the wall outlet and notplugged into the laptop. The requirements for less than30 mW of no-load input power is quite common in suchapplications like notebook, Ultrabook or printer adapters.Every loss component in the power supply design starts toplay a big role when trying to achieve such a small amountof no-load input power. Two important components ofno-load consumption are the controller consumption and theEMI filter X2 capacitor discharge branch.The NCP1244/46 family of PWM controllers hasintegrated advanced features which dramatically reduceconsumption in no-load mode. These are off-mode and theX2 capacitors discharge sequences which fulfill the safetyrequirements when the power supply is unplugged from theoutlet.The power supply having no-load consumption below30 mW can be designed using the NCP1244/46 family ofPWM controllers.

Features

• The NCP1244/46 Features Brief Description
• Comparison between the Adapter Design SolutionUsing NCP1236 without Off Mode with the DesignUtilizing the NCP1244/46
• The Off-mode Control Detailed Description
• X2 Capacitor Discharge System Description and itsCapability
• The Low Power Measurement Analysis of Precision
• The HV Pin Sensitivity to Noise
• Summary of the Obtained Results
• Reference Design

More information

• Datasheet
• IC product information